4 use utils::{snippet, span_lint_and_then};
6 /// **What it does:** Checks for variable declarations immediately followed by a
7 /// conditional affectation.
9 /// **Why is this bad?** This is not idiomatic Rust.
11 /// **Known problems:** None.
23 /// let mut baz = None;
33 /// let foo = if bar() {
39 /// let baz = if bar() {
46 pub USELESS_LET_IF_SEQ,
48 "unidiomatic `let mut` declaration followed by initialization in `if`"
54 impl LintPass for LetIfSeq {
55 fn get_lints(&self) -> LintArray {
56 lint_array!(USELESS_LET_IF_SEQ)
60 impl LateLintPass for LetIfSeq {
61 fn check_block(&mut self, cx: &LateContext, block: &hir::Block) {
62 let mut it = block.stmts.iter().peekable();
63 while let Some(stmt) = it.next() {
65 let Some(expr) = it.peek(),
66 let hir::StmtDecl(ref decl, _) = stmt.node,
67 let hir::DeclLocal(ref decl) = decl.node,
68 let hir::PatKind::Binding(mode, ref name, None) = decl.pat.node,
69 let Some(def) = cx.tcx.def_map.borrow().get(&decl.pat.id),
70 let hir::StmtExpr(ref if_, _) = expr.node,
71 let hir::ExprIf(ref cond, ref then, ref else_) = if_.node,
72 !used_in_expr(cx, def.full_def().def_id(), cond),
73 let Some(value) = check_assign(cx, def.full_def().def_id(), then),
74 !used_in_expr(cx, def.full_def().def_id(), value),
76 let span = codemap::mk_sp(stmt.span.lo, if_.span.hi);
78 let (default_multi_stmts, default) = if let Some(ref else_) = *else_ {
79 if let hir::ExprBlock(ref else_) = else_.node {
80 if let Some(default) = check_assign(cx, def.full_def().def_id(), else_) {
81 (else_.stmts.len() > 1, default)
82 } else if let Some(ref default) = decl.init {
90 } else if let Some(ref default) = decl.init {
96 let mutability = match mode {
97 hir::BindByRef(hir::MutMutable) | hir::BindByValue(hir::MutMutable) => "<mut> ",
101 // FIXME: this should not suggest `mut` if we can detect that the variable is not
102 // use mutably after the `if`
105 "let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
108 cond=snippet(cx, cond.span, "_"),
109 then=if then.stmts.len() > 1 { " ..;" } else { "" },
110 else=if default_multi_stmts { " ..;" } else { "" },
111 value=snippet(cx, value.span, "<value>"),
112 default=snippet(cx, default.span, "<default>"),
114 span_lint_and_then(cx,
117 "`if _ { .. } else { .. }` is an expression",
119 db.span_suggestion(span,
120 "it is more idiomatic to write",
122 if !mutability.is_empty() {
123 db.note("you might not need `mut` at all");
131 struct UsedVisitor<'a, 'tcx: 'a> {
132 cx: &'a LateContext<'a, 'tcx>,
133 id: hir::def_id::DefId,
137 impl<'a, 'tcx, 'v> hir::intravisit::Visitor<'v> for UsedVisitor<'a, 'tcx> {
138 fn visit_expr(&mut self, expr: &'v hir::Expr) {
140 let hir::ExprPath(None, _) = expr.node,
141 let Some(def) = self.cx.tcx.def_map.borrow().get(&expr.id),
142 self.id == def.full_def().def_id(),
147 hir::intravisit::walk_expr(self, expr);
151 fn check_assign<'e>(cx: &LateContext, decl: hir::def_id::DefId, block: &'e hir::Block) -> Option<&'e hir::Expr> {
153 block.expr.is_none(),
154 let Some(expr) = block.stmts.iter().last(),
155 let hir::StmtSemi(ref expr, _) = expr.node,
156 let hir::ExprAssign(ref var, ref value) = expr.node,
157 let hir::ExprPath(None, _) = var.node,
158 let Some(def) = cx.tcx.def_map.borrow().get(&var.id),
159 decl == def.full_def().def_id(),
161 let mut v = UsedVisitor {
167 for s in block.stmts.iter().take(block.stmts.len()-1) {
168 hir::intravisit::walk_stmt(&mut v, s);
181 fn used_in_expr(cx: &LateContext, id: hir::def_id::DefId, expr: &hir::Expr) -> bool {
182 let mut v = UsedVisitor {
187 hir::intravisit::walk_expr(&mut v, expr);